fix: use Map lookup for subgraph output disconnect

- Replace deprecated indexed link access with Map#get in SubgraphOutput.disconnect

- Add behavior-focused regression coverage for idempotent output disconnect

Amp-Thread-ID: https://ampcode.com/threads/T-019ca639-cde7-744d-b426-6ea21b2159e6
Co-authored-by: Amp <amp@ampcode.com>

src/lib/litegraph/src/subgraph/SubgraphIO.test.ts

@@ -565,6 +565,29 @@ describe('SubgraphIO - Output Slot Dual-Nature Behavior', () => {
       expect(internalNode.outputs[0].links).toEqual([])
     }
   )
+
+  subgraphTest(
+    'disconnect is idempotent and keeps output endpoints detached',
+    ({ subgraphWithNode }) => {
+      const { subgraph } = subgraphWithNode
+
+      const internalNode = new LGraphNode('Internal Source')
+      internalNode.addOutput('out', '*')
+      subgraph.add(internalNode)
+
+      const subgraphOutput = subgraph.outputNode.slots[0]
+      const link = subgraphOutput.connect(internalNode.outputs[0], internalNode)
+      if (!link) throw new Error('Expected link')
+
+      subgraphOutput.disconnect()
+      subgraphOutput.disconnect()
+
+      expect(subgraph.getLink(link.id)).toBeUndefined()
+      expect(subgraphOutput.getLinks()).toEqual([])
+      expect(subgraphOutput.linkIds).toEqual([])
+      expect(internalNode.outputs[0].links).toEqual([])
+    }
+  )
 })
 
 describe('SubgraphIO - Boundary Connection Management', () => {

src/lib/litegraph/src/subgraph/SubgraphOutput.ts

@@ -136,7 +136,7 @@ export class SubgraphOutput extends SubgraphSlot {
 
     //should never have more than one connection
     for (const linkId of [...this.linkIds]) {
-      const link = subgraph.links[linkId]
+      const link = subgraph.links.get(linkId)
       if (!link) continue
 
       const { outputNode } = link.resolve(subgraph)